Window blinds and net-curtains are invariably hung inside the window reveal and, where possible and convenient, are hung from brackets or fittings which are attached directly to the window frame.
In order to support window-blinds or net-curtains on window-frames or on door-frames, it is necessary in the first instance to attach a support bracket or other fitting to the frame. Where the window or door frame is made of solid timber the support bracket or fitting can be supported by passing a screw through the bracket or fitting and then driving the screw into the timber frame.
However window and door-frames are, generally, not constructed from solid timber or from any other solid material but are made from materials such as .mu.PVC, aluminium or composite materials not in solid form but in hollow multi-cavity form having a relatively thin outer wall and several separate longitudinal cavities inside.
FIG. 7 is a cross-sectional view of a known hollow multi-cavity .mu.PVC window frame.
The support bracket or other fitting required to support window-blinds or net-curtains on hollow frames cannot be successfully attached to the frame by means of a screw for the following reasons:
(a) the outer wall of the .mu.PVC window or door frame is usually not more than about 3 mm thick; PA1 (b) the outer wall of an aluminium window or door frame is usually not more than about 1.5 mm thick. PA1 (a) in view of the fact that the outer wall of the frame is relatively thin and relatively weak, the fitting must be capable of providing a wide load-bearing surface to the rear of the face material. Preferably, the load-bearing surface must be wider than the typical first cavity in a hollow frame is deep; PA1 (b) in view of the relatively shallow nature of the first cavity in the frame and the unacceptability of breaching the second cavity, the fitting must be capable of operating in a cavity no greater than about 5 mm deep i.e. it should not be necessary for the fitting to protrude more than 5 mm behind the front wall of the frame; PA1 (c) the fitting must not require to be placed fully home in the hole in the host material before being deformed. Preferably, it should be capable of being deformed progressively as the fitting is fed into the hole; PA1 (d) the fitting should be capable of being used in a cavity which is not as deep as the fitting is long; PA1 (e) the fitting should be incapable of becoming wedged partly in and partly out of the hole in the host material; PA1 (f) the fitting should be capable of being placed as close as 7 mm from the side wall of the window reveal; PA1 (g) the fitting should adjust automatically to unpredictable obstructions inside the first cavity of the frame e.g. side walls of upper or lower cavities; PA1 (h) the fitting should be capable of withstanding relatively heavy loads which tend to withdraw the fitting from the frame and must do so without damaging or marking the frame; PA1 (i) the fitting should be capable of being applied with a tool which is easy to use and which can be relatively inexpensive to manufacture; PA1 (j) the fitting should be capable of re-use i.e. the screw attaching the bracket or other fitting to the fixing should be capable of being removed and reliably replaced in the event of the bracket being removed; PA1 (k) the fitting should lock in relation to the outer wall so as not to fall into the cavity in the event of a screw being placed in the fixing with excessive inward force; PA1 (l) the fitting should provide a virtually flush fit with the outer surface of the outer wall of the frame; and PA1 (m) the fitting should be capable of application by relatively unskilled operatives. PA1 requires a deeper cavity than is available; PA1 does not provide a sufficiently flush finish on the surface of the face material; PA1 does not adjust to internal obstructions; PA1 requires to be placed fully home in the hole before it is compressed otherwise it is liable to become wedged partly in and partly out of the hole. PA1 (a) it involves a degree of skill and equipment which makes it necessary for many householders to engage a professional fitter and thus expense; PA1 (b) the process is generally slow, labour-intensive and therefore expensive; PA1 (c) the process interferes with decoration and causes a cascade of plaster and concrete dust in the room; PA1 (d) the fitter does not know until he drills the hole whether his attempt will in fact find solid ground to support the rawl-plug and screw; frequently he encounters dry-lining with brittle unsupporting plaster and a hollow cavity, a steel girder or a pre-cast lintel. The fitter is then obliged to abandon the first attempt and endeavour to make good the decoration and try again, hopefully this time to succeed but perhaps not; PA1 (e) the problems are compounded where more than one hole must be drilled at an exact distance from another hole. This arises where brackets for window blinds are being fitted in which there are usually at least two holes required. If the second hole in the plaster is unsuccessful then both it and the first hole must be abandoned, the decoration made good and a new site tried; PA1 (f) fitters, whether amateur or professional, prefer to attach fittings with the minimum of trouble and the maximum of security. They would prefer not to drill and screw but if they have to drill and screw they prefer a predictable medium like timber.
These wall thicknesses are insufficient to give a screw the long term grip required to hold support brackets for window blinds or fittings for net-curtains. Furthermore, the main internal cavity in the frame is sealed against moisture and must not be breached by a screw which is driven into the frame and, thus, the screw can only penetrate the outer wall of the frame and must not penetrate beyond the first cavity of the frame.
Where screws are used by a window manufacturer to apply attachments a .mu.PVC frame, then the .mu.PVC must be of double thickness at the point where the screw enters the frame. Manufacturers of window-frame material do not generally provide double wall thickness where support brackets or fitting might be expected to be attached for the support of window-blinds or net-curtains.
Consequently, screws should not be, and generally are not, used to attach brackets or fittings to .mu.PVC or to aluminium window or door frames.
While inappropriate improvised methods and materials are sometimes used by DIY enthusiasts, professional fitters of window-blinds and net-curtains do not attach support brackets or fittings directly to hollow frames by means of screws.
As an alternative to driving a screw directly into a relatively thin or relatively weak sheet material, various `cavity-fixings` are available for general purposes. These general purpose cavity fixings provide a variety of ways of attaching a solid or threaded medium to the thin or weak sheet which medium is then capable of receiving and retaining a screw.
General purpose cavity fixings are successful in many thin or weak sheet applications. However because of the special constraints associated with hollow frames, general purpose cavity fixings cannot be used successfully to support window-blind brackets or fittings for net-curtains on such frames.
To be suitable for use in typical hollow frames a cavity mounting device should preferably have the following characteristics:
FIG. 1 shows an example of a known fitting which comprises a hollow tapered body 500 with side splits, a plurality of sharp projections on the exterior and screw threads on the interior.
After the known fitting 500 of FIG. 1 is placed in the hole in the material 501, a screw 502 is threaded into the fitting causing the fitting to expand outwards thus causing the sharp projections to penetrate into the side of the hole in the host material.
The fitting of FIG. 1 is not suitable for use in the outer wall of hollow frames as the projections grip with short teeth and only into the range of the wall thickness of the outer wall which is no more than 3 mm. It does have a function for use with very light loads.
FIG. 2 shows an example of a known fitting which comprises a hollow tapered body 600 with side splits and having internal and external threads, the external threads being of a greater height at the broad end of the fitting. After the fitting of FIG. 2 is screwed into the hole of the material 501, a screw 502 is threaded into the fitting causing the fitting to expand and the external threads to lock deeper into the host material 501. The fitting of FIG. 2 is not suitable for use in the outer wall of hollow frames as it is not capable of carrying the required load without pulling out of the host material. The grip range is limited to the thickness of the outer wall which is not more than about 3 mm. It does have a function for use with very light loads.
FIGS. 3 and 4 show an example of a known fitting which comprises a hollow body 700 the interior lower part of which is threaded. A screw 502 or pulling mandrel is fitted into the internal threads thereof and is used to compress the fitting which, as a result, bulges out behind the face material 501. The bulge 701 resists withdrawal of the fitting. This fitting is normally used in sheet metal but is not suitable for use in weaker material through which it will pull under load as it does not have a wide load-bearing area behind the face material.
FIGS. 5 and 6 shows a known fitting 800 which comprises a head 801 and a threaded end portion which are joined by a plurality of collapsible arms.
A screw 502 or pulling mandrel is fitting into the internal threads and is used to compress the fitting as a result of which collapsible arms 802 collapse outwards behind the face material.
The fitting of FIGS. 5 and 6 provide a wide load-bearing area to the rear of the face material but is not suitable for use in hollow frames as it:
Other known cavity anchors are available but they either exhibit at least one of the flaws mentioned in relation to the examples at FIGS. 1 to 6 above and/or none enjoys characteristics which would render it suitable as a cavity anchor for use in hollow frames.
Other techniques which have been tried and found to be less than successful include self-adhesive pads (they tend to fall off) and telescopic tension-rods from which curtains on non-curved windows may be hung. However, this arrangement is not suitable for blinds.
To overcome the problems associated with the above identified known fittings, window-blind fitters and householders are compelled to drill into the plasterwork above or to the side of the window frame in order to attach a fitting with a rawl type plug and a wood-screw. This results in serious disadvantages:
Unfortunately, the most popular window frames today (aluminium and .mu.PVC frames) do not provide such a medium. The medium cannot support a screw and cannot easily be repaired or filled.
It is an object of the present invention to overcome or mitigate these problems.
Accordingly, there is provided a mounting device as claimed in claim 1.